Our program project consists of four projects and three cores which focus on the border zone and three cores which focus on the border zone in acute ischemia. The projects employ in-situ porcine heart, isolated perfused rabbit papillary muscles, cultured rat myocytes, and lipid bilayers, to monitor, model, and mimic the ionic/electrophysiologic changes which occur at the ischemic border and which result in ventricular fibrillation and sudden cardiac death. Dr. Gettes' project correlates the ionic and electrophysiologic events at the border zone in the in-situ porcine heart, with specific reference to areas of very slow conduction and potentially short reentry circuits, and determines as precisely as possible in the isolated perfused rabbit papillary muscle, the cause of the changes in action potential characteristics, conduction, and refractoriness, which occur at ischemic borders. Dr. Cascio evaluates the role of diffusion of gases, substrates, metabolites and vasoactive factors across the ischemic border on the ionic/electrophysiologic changes. It employs confocal microscopy in the perfused rabbit papillar muscle and a unique planar model of cultured rat myocytes. It pays particular attention to changes in intracellular calcium and pH and to the possibility of propagating calcium waves. Dr. Rosenberg studies the sarcolemmal L-type calcium channel incorporated into lipid bilayers to characterize the molecular mechanisms responsible for modulating these channels along ischemic borders. It mimics the conditions in the ischemic border by controlling the extracellular and intracellular ionic metabolic, and enzymatic conditions on both sides of the membrane to gain information which will help explain the electrophysiologic changes studied in projects. Dr. Meissner's project utilize lipid bilayers and the perfused rabbit papillary muscle to study the relationship between the protein structure of the calcium release channel in the sarcoplasmic reticulum and its regulation. It tests the hypotheses that the channel is multi-ligand gated, that the calcium is the principal regulator of the channel, and that changes in the intracellular ionic milieu associated with acute ischemia cause changes in channel function. The program involves investigators from the Departments of Medicine, Biochemistry, Biophysics, Cell Biology, Anatomy, Pharmacology, Biomedical Engineering, and Biostatistics, and extensive collaboration with investigators at North Carolina State University. The National Institutes for Environmental Health Sciences, Duke University, and the Universities of Bern and Amsterdam. We believe that the sharply focused and integrated studies which comprise our program will provide important new information concerning the role of the ischemic border zone in sudden cardiac death.